Solve for $x$ and $y$ using substitution. ${3x-y = -9}$ ${y = -5x-7}$
Explanation: Since $y$ has already been solved for, substitute $-5x-7$ for $y$ in the first equation. ${3x - }{(-5x-7)}{= -9}$ Simplify and solve for $x$ $3x+5x + 7 = -9$ $8x+7 = -9$ $8x+7{-7} = -9{-7}$ $8x = -16$ $\dfrac{8x}{{8}} = \dfrac{-16}{{8}}$ ${x = -2}$ Now that you know ${x = -2}$ , plug it back into $\thinspace {y = -5x-7}\thinspace$ to find $y$ ${y = -5}{(-2)}{ - 7}$ $y = 10 - 7$ $y = 3$ You can also plug ${x = -2}$ into $\thinspace {3x-y = -9}\thinspace$ and get the same answer for $y$ : ${3}{(-2)}{ - y = -9}$ ${y = 3}$